If they haven't benchmarked their site on my computer, they don't know whether it's making their websites more performant. But years of experience with JS disabled by default (and only enabled when necessary) makes it very clear to me that using JS, at least on my system, is almost never a way to make any site more performant. On the contrary, it increases load times, cpu usage, and memory usage. It might also force me to use bloated crappy browsers like Firefox or Chrome where I could otherwise use something like w3m or links, which will display the page in a fraction of the RAM, much faster.

I wouldn't be disabling JS if it weren't such a pain in the ass. Or maybe I still would, just for security.